Polyalkenamers

The term polyalkenamer has been applied to hydrocarbon polymers of the type  

This definition is usually extended to embrace polymers in which one or more of the hydrogen atoms in the basic polyalkenamer structure are substituted by alkyl, aryl, halogen or other groups. Thus polybutadiene, polyisoprene and polychloroprene may be considered as particular members of this group. 

These three rubbers are of course produced commercially by polymerization of a diene. Polybutadiene however may also be 

It is the ring-opening process which has in recent years enabled new polyalkenamers to be prepared. The polymers have low TgS, are regular and potentially crystallizable and are capable of sulphur vulcanization. 

The ring-opening process involves a metathesis reaction in which two cyclo-olefinic double bonds are simultaneously cleaved, this being followed by transalkylidenation of the fragments. Thus for cyclopentene the process may be represented as  

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Of these various groups there was extensive interest for some years in polyalkenamers such as frani -polypentenamer which has now abated whilst interest in polynorbomene is steadily increasing. Since the chemistry and technology of the two types is somewhat different each type will be dealt with separately. A third group comprises the chlorine-containing polymers announced by Goodyear in 1980. 

The polyalkenamers are usually prepared by means of a Ziegler-Natta catalyst system. For example fran.v-polypentenamer may be obtained from cyclopentene... 

As a class the aliphatic polyalkenamers have low values due to a combination of low chain stiffness and low interchain attraction. The presence of double bonds has the effect of increasing the flexibility of adjacent single bonds (see Chapter 4) and overall this leads to a reduction in. Thus in the sequence from polydecenamer down to polypentenamer an increase in the double bond concentration leads to a lowering of Tg. On the other hand the Tg of polybutenamer, i.e. poly butadiene, is somewhat higher than that of polypentenamer, presumably because the proportion of stiff links, i.e. double bonds, becomes sufficiently high to override the flexibilising effect on adjacent chains. Consequently the polypentenamers have the lowest Tg values known for hydrocarbon polymers (cis- -114°C, trans- -97°C). 

Cyclic dienes and polyenes, monocyclic as well as bicyclic, can be metathesized in the same way as cyclic monoenes. As expected, cyclobutene 27), 1,5-cyclooctadiene, and 1,5,9-cyclododecatriene 28) yield the same polyalkenamer, in this case polybutenamer (1,4-polybutadiene), since these reactants consist of the same base units, i.e.—(CH2)2CH==CH— ... 

EPM > CO > TP > CB. The highly crystalline TB had an etch rate about six times that of CB, ascribable to a morphology difference, while the partially crystalline TO had an etch rate somewhat higher than that of amorphous CO. Cis/trans content had little or no effect on the etch rate of the polyalkenamers. A mechanism involving crosslinking through vinyl units is proposed to explain the unexpected protection imparted to vinylene-rich polybutadienes by the presence of 1,2 double bonds. 

Figure 5. Typical kinetic plots for 0(3P)-induced weight loss in various polybutadienes and polyalkenamers.

Polyacetylene, vibrational spectra, 42 196 Poly acids, defined, 41 117 Polyalkenamers,24 134,135 Polyamino acids, thermal, 20 374-377 catalysis by, 20 379... 

Among others, it can be used in ring-opening metathesis polymerization to produce polynorbomene the oldest polyalkenamer (see Section 12.3). Cycloaddition of... 

Polynorbomene the oldest polyalkenamer is manufactured by a method developed by CDF Chimie156 157 since 1976. Tungsten or rhodium catalysts are used to yield a highly trans polymer. This is capable of rapidly absorbing hydrocarbon oils and can be crosslinked to produce a very soft rubber. 

Isomorphism in copolyalkenamers was reported by Dall Asta, Motroni, and Carella (27). These copolymers may be considered as constituted by an unbranched polyethylene chain containing, at irregular intervals, fra s-intemal double bonds. It is known 28) that the crystal structure of the homo-fraws-polyalkenamers depends on the number of methylene groups existing between two subsequent double bonds the odd series crystallizes in an orthorhombic unit cell, similar to that of... 

With cyclic olefins as the reactants, disproportionation results in ring enlargement leading to the formation of macrocyclics and, ultimately, polymeric materials, i.e., polyalkenamers (Reaction 3). 

The products of the ring-opening metathesis polymerisation of cycloolefins, poly(l-alkenylene)s, are known as polyalkenamers according to the nomenclat-... 

In ROMP cyclic olefins are polymerized to polyalkenamers. Both 1 and 3 can be used for this reaction, but catalyst 3 was found to be significantly more efficient for the polymerization of cyclooctene derivatives (Eq. 13) [30]. Polymerization commences with initiation of the catalyst through dissociation of a neutral ligand such as a tricyclohexylphosphine for 1 and 3 (see... 

The metathesis products, the polyalkenamers, exhibit excellent properties as polymeric fillers for elastomers. The interests of the rubber industry stimulate research orientation to this kind of ring-opening polymerization (see, for example, refs. 344-346). 

ROMP processes are unique in that they offer unsaturated polymer products with properties between those of saturated polyethylene and the highly unsaturated polybutadienes. These polyalkenamers have been the subject of intense study by companies dealing in speciality polymers. In the 1970 s the ROMP product of cyclopentene attracted attention as a replacement for natural rubber, due to its good strength and ageing properties. Although the elastomer was never commercialized, as its overall characteristics did not meet requirements, the work stimulated research into ROMP of other cyclic alkene... 

It is part of a homologous series of linear unsaturated polymers that are termed polyalkenamers. Polypentenamer is an interesting member of this series because cyclopentcne is economically available from petrochemical by-products and because the polymer is a readily vulcanizable elastomer (since it contains residual C—C double bonds cf. p. 10). 

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